Simple GO TCP proxy

proxy.go

package main 
import ( 
        "net" 
        "fmt" 
        "io" 
        "os" 
) 
func main() { 
        if len(os.Args) != 3 { 
                fatal("usage: netfwd local remote") 
        } 
        localAddr := os.Args[1] 
        remoteAddr := os.Args[2] 
        local, err := net.Listen("tcp", localAddr) 
        if local == nil { 
                fatal("cannot listen: %v", err) 
        } 
        for { 
                conn, err := local.Accept() 
                if conn == nil { 
                        fatal("accept failed: %v", err) 
                } 
                go forward(conn, remoteAddr) 
        } 
} 

func forward(local net.Conn, remoteAddr string) { 
        remote, err := net.Dial("tcp", "", remoteAddr) 
        if remote == nil { 
                fmt.Fprintf(os.Stderr, "remote dial failed: %v\n", err) 
                return 
        } 
        go io.Copy(local, remote) 
        go io.Copy(remote, local) 
} 

func fatal(s string, a ... interface{}) { 
        fmt.Fprintf(os.Stderr, "netfwd: %s\n", fmt.Sprintf(s, a)) 
        os.Exit(2) 
} 

perfect ✌️

awesome

a small change, local and remote will Close() at the same time if one part disconnected.

package main
import (
        "net"
        "fmt"
        "io"
        "os"
)
func main() {
        if len(os.Args) != 3 {
                fatal("usage: netfwd local remote")
        }
        localAddr := os.Args[1]
        remoteAddr := os.Args[2]
        local, err := net.Listen("tcp", localAddr)
        if local == nil {
                fatal("cannot listen: %v", err)
        }
        for {
                conn, err := local.Accept()
                if conn == nil {
                        fatal("accept failed: %v", err)
                }
                go forward(conn, remoteAddr)
        }
}

func forward(local net.Conn, remoteAddr string) {
        remote, err := net.Dial("tcp", remoteAddr)
        if remote == nil {
                fmt.Fprintf(os.Stderr, "remote dial failed: %v\n", err)
                return
        }

        go func() {
            io.Copy(local, remote)
            local.Close()
            remote.Close()
        }()

        go func() {
            io.Copy(remote, local)
            remote.Close()
            local.Close()
        }()
}

func fatal(s string, a ... interface{}) {
        fmt.Fprintf(os.Stderr, "netfwd: %s\n", fmt.Sprintf(s, a))
        os.Exit(2)
}